Interestig question..and antos nonxox actually froces me right now to attack the topic once more..
Just removing all the mods and bring the xox back to a clean state..
Some mods that got it more 303 alike i keep or intensivate.
Following problems got eliminated since i got it years ago..
Roland 662 VCA ..selected..they all sound different.. but make a more mushy sound as we know it from the 303.. the newer chip is clearer and snappier. I like it actually..but dont works in facor of the anyway harder xoxbox sound
2) original foil caps in the filter.. The original ones are transparent green drops and these give a finer sound that the ceramic tile style green drops.. these sound indeed harder..
I also checked various other types.. even much better ones than the originals..theese deliver aswell a very fine tone..but extended high frequency response…what dont works in favor of the xox hardness..
So the original transparent green was the best i could find.. i robbed other old roland machines to get them..
3) Old semiconductors.. I got my parts from a trustworthy guy. but..how good are modern batches of discontinued transistors? Are they remakes? fakes? .. I got a big step smoother by sourcing old transistors in old VCR and Hifi equipment. In 100% of the cases the older parts was giving a warmer and smoother sound… Maybe i really had remade versions? I know fake chips.. theese usually dont work very good at all..but on the single transistor it maybe works but sounds harsher?
4) Transistor type? What is the best sounding one? I am still uncertain..except again that old versions sound different than new batches.. that is especially visible on transistors still produced ..sinnce they are to available to get faked… A topic i actually would like to discuss.. My xox is 945 based …but i ve a handfull old 1815/1015 available..according to what i just wrote the old 1815 are brobably better than new 945..even when new 945 are better than new 1815..
That the question i maybe try to answer now…since i really hate that my xox sounds not 303 alike even after all this changes..
5) Resistor type … you need to use the resistors specified by ada fruit.. metal film gives a harder sound.
6) other factors?
internal gate timing?
power supply circuit?
internal HF polution by usb chip and higher takt..or the relative absence of hf polution and noise by the missing dc/dc converter and its 70khz interference?
stray capacitys? the original board is way smaller and has not as much shielding as the xox board..
that is pico farads here and there thru the circuit and areas of potential low level crosstalk fx..even crosstalk on the modulation is thinkable..resulting in slightly different envelope shapes.
This are the 4 suspects i ve left..or what else could harden the sound of the xox so much?
I actually fear that it is a combination of all this aspects and therefore a 100% 303 is reserved for the 303..
But its thinkable that further optimisations are possible.. See the TT bassbot that has so many sgit sounding component choices that it actualy shoudl sound even more shrill and hard as a xox.and it actually does..but has a certain elasticity i miss on the xox..i wonder if this is the impact of the power supple..and a xox with bassbot style original power supply would give a decend result..
Problem..where to get the parts for an original power supply? or shall i slaughter my 303 to isolate its power supply from its circuit to feed the xox with it? actually i dont love ,y xox enough to do this.. maybe i should lend a 606?